Method for manufacture of non-allergy creating precious metal objects

ABSTRACT

A method for manufacturing a non-allergenic metal object which can be safely worn next to the skin, comprising the steps of: providing an optimum pure starting material selected from a class comprising an optimum pure nobel metal and an optimum pure noble-metal alloy; creating a protective atmosphere at atmospheric pressure and consisting of water-free hydrocarbons incompletely combusted with pure oxygen and free of oxygen, hydrogen, nitrogen and nitrogen oxides; melting the starting material in the protective atmosphere; molding a molded object from the starting material in the protective atmosphere; solidifying and cooling the molded object in the protective atmosphere; the step of annealing the solidified molded object prior to cooling and including the further steps of heating the protective atmosphere and causing it to flow in one direction, moving the solidified molded object through the heated flowing protective atmosphere in the opposite direction, maintaining a portion of the heating flowing protective atmosphere sufficiently hot to effect annealing of the solidified molded object, and maintaining another portion of the heated flowing protective atmosphere sufficiently cool to allow cooling of the annealed molded object.

This is a divisional application of U.S. Ser. No. 099,661, filed Sept.21, 1987 now U.S. Pat. No. 4,902,342; which is a continuation of Ser.No. 626,876 foled PCT SE83/00371 on Oct. 28, 1983 published asWO84/01788 on May 10, 1984, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a method and an apparatus for themanufacture of non-allergenic creating objects of precious metals. Byprecious metal objects are meant any type of objects which arecompletely or partly made of a precious metal or a precious metal alloy,and the invention is especially concerned with such objects which aresupposed to get in contact with the skin of a human body, for instancefinger rings, bracelets, jewel chains, brooches, amulets, earrings,watches, glasses and sun-glasses etc. The precious metal may be gold,silver, platina, rodium, palladium and other precious metals suited forthe manufacture of the above mentioned objects. The precious metals maybe solid or may be in the form of double or any other surface coveringof some less precious metal like copper, zinc, aluminum, tin or chromeor nickel or any alloy of such metals. According to the invention theobject also may be made as a whole of these non-precious metals.

It is known that many people are hit by different kinds of illnessconditions at skin contact with jewels, watches, glasses and many otherobjects made of the said metals. Special troublesome phenomena mayappear when the said objects get in contact with very thin skin withhigh transmittance get in contact with very thin skin with hightransmittance ability like for instance rings, especially earringsapplied through holes in the ear tip. The illness conditions generallyare skin troubles like itching, scorching, eryphema, exanthena, liquidcontaining blisters or suppuration boils. In addition to such skintroubles more intense illness conditions may appear.

Test have proven that the said illness conditions which generally arereferred to as allergic affections do not appear if the object incontact with the human skin is made of optimum pure and clean metals ofgold, silver, platinum (platina), rodium, palladium etc. not even if thesaid metals have been alloyed with optimum pure and clean copper, zincor tin or even aluminum, nickel or chrome. There are reasons to believethat the said allergic affections depend on impurities in the metal orthe metal alloys. It may be assumed that some alloy substances causeserious allergic affections, like for instance alloyed heavy metal likecadmium, lead, mercury, bismuth, antimony, cobalt, etc. Allergicaffections also may appear if impure alloy metals are used like impurecopper, zinc, tin or any other impure alloy metals. Impurities mayappear both when manufacturing the precious metal or the precious metalalloy itself or during the working and the following treatment of themetal of the metal alloy. For instance impurities may be added in theprecious metal, the alloy metal or the alloy if treated with an acidduring the manufacture or the subsequent treatment. Copper has a greattendency of assimilating many different types of impurities. Without therisk of the appearance of allergic problems, optimum pure and cleancopper, optimum pure zinc, optimum pure tin and possibly even optimumpure aluminum, chrome or nickel and other metals may be used as alloymetals. On the contrary it is of great importance that most types ofheavy metals and thereby related or similar metals like cadmium, lead,mercury, bismuth, antimony, cobalt etc. are completely excluded from thealloy.

It is also of importance to eliminate the impurities and any furthermetals or any other allergy creating substances in the base metal ofobjects covered with precious metals, so called double objects orobjects coated in any other way. All metals are more or less "leaky",and by metal transient movements heavy metals and impurities and otherallergy creating substances in the base of a double object or an objectcoated in any other way may be released from said base and may movethrough the precious metal layer and dispose as a surface covering ofthe object. By the invention it has also been shown that, for instance,cadmium has a great tendency for such metal transient movement. Cadmiumalloyed objects therefore generally get a more or less thin surfacecovering of the allergy creating heavy metal cadmium.

In the manufacture of objects of non-alloyed precious metals or preciousmetals alloyed with optimum pure alloy metals like copper, zinc, tin andeven chrome or nickel, there often arise manufacturing technicalproblems.

As an example, silver in combination with copper has a so-called shapememory, and as a consequence when heat treating a cold worked silverobject the object tends to regain the form that the silver object hadbefore the cold working. Such shape memory causes large problems forinstance when soldering the objects in that the joint opens when theobjects is heated and there is a risk of bad soldering. In order toneutralize the shape memory of the silver and to make the silver shapewilling, cadmium generally is added to the silver. Often an addition ofmore than 7% cadmium was needed in order to obtain the intended effect.When adding cadmium to the silver, a brittle soldering joint isobtained. An addition of cadmium in a silver alloy however, givesserious allergy problems. Equivalent problems appear when manufacturingobjects of gold, platinum (platina), palladium, rodium and otherprecious metals as well as when manufacturing objects of copper, zinc,aluminum, tin and even nickel or chrome or alloys like brass or tombak.

When performing stress-relieving annealing, salts generally are used,so-called hardening salts. The salts may be hot or cold. For the purposeof cooling the metals in connection to stress-relieving annealing, watermixed with certain salts often is used for raising the evaporatingtemperature. Also, such salts may cause allergic affections, and it isalso important to forsee that the metal object does not get in contactwith such salts.

SUMMARY OF THE INVENTION

The object of the invention therefore is to solve the problem ofproviding a method and an apparatus for manufacturing of objects of puremetals, especially precious metal alloys or alloys of pure preciousmetals and optimum pure alloy metals like copper, zinc, aluminum, tin,chrome, nickel, etc.

So far it has not been considered possible to manufacture objects ofsuch pure metals and pure metal alloys depending on the above mentionedmanufacturing problems. Surprisingly it has, however, proved that it isnot only possible to use such pure metals but by special working metalsand the use of special apparatus for working the metals and the metalobjects it is even possible to obtain objects without any noticeableshape memory and having a rupture strength which is even higher than forpreviously known metals or metal alloys which are alloyed with cadmiumor other heavy metals, in which the alloys include impure preciousmetals or alloy metals. By the method and the apparatus according to theinvention it is also possible to obtain soldering joints which are moretenacious and have a substantially higher rupture strength than thejoints which are obtained in objects made of cadmium containing alloys.

The method and the apparatus according to the invention are based on thepresumption that optimum pure metals are used, which metals are mixed,alloyed and worked in heated condition without any contact with theambient air.

In the method according to the invention only optimum pure metals suchas precious metals like gold, silver, platinum, palladium, rodium etc.and alloy metals like optimum pure copper, zinc, aluminum, tin and evennickel and chrome are melted and alloyed. In order to make sure that themetals are real optimum pure, some reduction agent may be added forabsorbing possible impurities. The said reduction agent becomes a slaglayer on the surface of the melted metal, which slag layer prevents theair from getting into contact with the metal. Further the metal ispreferably molded under a protective gas and under the said reducingslag layer in order to prevent the oxidization. The blank therebyobtained is cold worked and is stress-relieving annealed, likewisewithout contact of external agents, for instance without the contactwith salts. Rather than using so-called hardening salts for coolingpurposes any of the following substances may be used: optimum purifiedwater (de-ionized water), optimum purified alcohol, a mixture ofpurified water and purified alcohol. Independently of what mixture isused the purity must be at least 0.1 us/cm².

The stress-relieving annealing must be done under protective gas orotherwise so that the access of air is prevented. Soldering and otherfurther heat treating also must take place without the access of air,and as a final product an object is obtained which is made of puremetals, especially pure precious metals and pure alloy metals, whichobjects may be considered completely non-allergic.

Now the method and the apparatus is to be described in connection to anumber of method stages and with reference to the accompanying drawings.

It is, however, to be understood that the method and the apparatusaccording to the invention is not restricted to the followingdescription and that the embodiments of the invention shown in thedrawings are only of an exemplifying character and that many differentmodifications may be presented within the scope of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an appartus for melting of metals in accordance with theinvention;

FIG. 2 shows a combined apparatus for melting of metals and for moldingand cooling of a molded metal rod;

FIG. 3 shows an apparatus for molding of melted metal according to theinvention;

FIG. 4 shows an appartus for stress-relieving annealing of a rod;

FIG. 5 shows an apparatus for annealing of a non-allergic creating metalwire;

FIG. 6 shows another apparatus for stress-relieving annealing of a woundring of metal wire;

FIG. 7 shows an apparatus for soldering of a metal chain according tothe invention; and

FIG. 8 is a cross-section along line VIII--VIII of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT Melting Step

The most important feature of the invention is that optimum pure metalsare used and that the total working of the metal or the metal alloy ismade so that no impurities are added during the working. As jewel metalsare in a first hand considered gold, silver, platinum (platina),palladium, rodium and other precious metals which may have been alloyedto each other or to alloy metals, in the first had copper zinc or tinbut even aluminum, nickel and chrome. All alloy metals must be optimumpure and not in any way treated in the surface. Previously it wasconsidered desirable or necessary that some types of heavy metals orsimilar material to be added, for instance, cadmium, lead, mercury,bismuth, antimony or cobalt. According to the invention it is, however,of extreme importance that no such heavy metals are allowed to be mixedinto the metals or metal alloys, neither during the continued treatment.In order to make sure that no impurities remain in the melted metal orare added during the melting operation a slight amount of some reductionagent is added, which agent absorbs such possible impurities andprovides a slag layer, which is kept on the surface of the melted metal.A suitable reduction agent in the form of a melting powder having anexcellent property to force impurities out of the melted metal is amixture of one part of potassium carbonate and 1.5 part of water-freesodium carbonate. The slag layer thereby obtained also has the importantpurpose of preventing the access of air during the continued melting andcooling of metals. The melting together of the metals is made withoutany access of air, for instance in that a protective gas is continuouslyblown over the metal surface or that the melting is made by means of aflame which covers the entire surface and prevents the access of air. Itis also possible to make use of the supply of protective gas and acovering flame.

In FIG. 1 shows a crucible, especially a graphite crucible 1 having alid 2 which is connected to a positive pole of current and having abottom 3, which is connected to a negative pole of current. The cruciblealso may have an alternative current heating. The lid is closed by astopper 4. In the lid or any other high position of the crucible thereis also a gas inlet 5 for protective gas and an outlet 6 for theprotective gas. Further there is a spout 7 in the lid which is closed bya spout stopper 8. In the crucible there is melted metal 9, which isheated electrically in that the current is brought to pass the graphitecrucible from the positive lid 2 to the negative bottom 3.

It is important that the metal is melted without access of air, and inthe described embodiments this is done in that the air is forced out andis substituted by protective gas which enters from the gas inlet 5 andfills the entire volume above the surface of the melted metal 9 andleaves through the gas outlet 6.

A suitable protective gas is obtained by burning water-free acetylenegas or methane gas together with a controlled amount of water-free pureoxygen in a combustion chamber 10. Instead of fusing pure oxygenwater-free compressed air may be used. In this case the purity isslightly less and the heating follows more slowly depending on thecooling effect of the nitrogen gas component. The combustion is madewith deficit of oxygen and the amount of oxygen is controlled so thatthe exhaust gas outlet at the gas outlet 6 contains un-combusted gaseswhich may be lighted, whereby a very thin blue colored flame 11 appears.By this method an atmosphere is created inside the combustion chamberand thereby also inside the gas volume 12 above the surface of themelted metal 9, which volume is absolutely free from oxygen, hydrogen ornitrogen gas.

A protective gas of the above-mentioned type can be used in allconditions during heat treatment of the metal object. When melting metalunder atmospheric pressure as shown in FIG. 1, the entire gas volume 12of the crucible is percolated by the combustible exhaust gas from thecombustion chamber 10 and the surface of the melted metal 9 iscontinuously spray washed with the said combustible exhaust gas. If onthe contrary, the melting and the molding is made under vacuum all gasvolumes firstly must be percolated by the combustible exhaust gas orprotective gas, and not until the gas volume has been percolated thevolumes are subjected to vacuum.

Molding Step

The melted metal or the metal alloy is molded into blanks without accessof air, preferably under protective gas underneath the reducing slaglayer for preventing oxidization. The molding of melted metal can bemade in a mold, for instance a tube which is preferably rubbed with oil.The entire tube is surrounded by a flame or a protective gas whichprevents the access of air. The melted metal evaporizes the oil on thewalls of the tube, and also the oil gases thereby obtained provide aprotective gas which contributes to protecting of the metal againstaccess of air. As oil for the mold tube previously used were animal oilslike lard fat, etc. Also, castor oil or asphalt based oils have beenused. The castor oil, however, quickly turns rancid, and the asphaltbased oils, in turn, give harmful effects. According to the invention itis suggested to use a paraffin based oil which gives a well protecting,inert protective gas layer and which has no harmful influence on thecontinued treatment of the metal. A blank molded under paraffin basedoil exhaust gases gets very good soldering joints during the continuedtreatment.

FIG. 2 shows a combined apparatus for melting and molding of metal undervacuum. The apparatus comprises a carrier 13 which at the bottomcontains a cooling liquid 14 of the previsously described type and whichabove the level of the cooling liquid carries a mold, for instance amold tube 15, which at the top has an inlet 16 for protecting gas and atthe bottom has a drop shutter 17 for letting the molding metal out. Ontop of the mold tube 15 a mold crucible of the same type as in FIG. 1 isplaced. The mold crucible 1' in which the melted metal 9' is heated hasa gas inlet 5' and a gas outlet 6' for the exhausted protective gas. Atthe top the mold is closed by a stopper 4', and at the bottom thecrucible has a pouring spout which is closed by a spout stopper 18. Thecarrier 13 encloses the entire apparatus as an air sealed unit. Betweenthe level of the cooling liquid 14 and the mold tube 15, there is aninlet 19 for combustion gas and oxygen which inside the carrier iscombusted under deficit of oxygen thereby providing a protective gas.The protective gas percolates the entire carrier between the mold tube15 and the carrier walls, and the protective gas also flows into the gasinlet 15 of the crucible 1' and out through the gas outlet 6' wherebythe gas is lightened, whereby the weak blue flame indicates the deficitof oxygen of the protective gas inside the apparatus.

When using the apparatus in FIG. 2, the crucible 1' is closed by meansof the spout stopper 18' and metal and possible reduction agent isfilled into the crucible. Combustible gas and oxygen is supplied throughthe gas inlet 19, and the protective gas is allowed to force the air outof the equipment. The lid 2' and the bottom 3' of the crucible 1' areconnected to a source of power, whereby the metal and the reductionagent are melted. At this stage the drop shutter 17 is kept open andprotective gas, which may be supplied from a branch conduit 20 to theprotective gas chamber 21 is blown through the gas inlet to the moldtube 15, whereby the protective gas forces the air out of the tube. Asusual the channel of the mold tube 15 should be conically widened in thedirection downward in order to facilitate the releasing of the moldblank from the mold 15.

Molding Step

When the metal 9' is melted the drop shutter 17 is closed, and the gasinlet 16 now is connected to a vacuum pump which sucks the protectivegas out of the mold chamber 22 of the mold tube 15. The pouring spout 18of the crucible is lifted and the melted metal 9' is allowed to flowdown into the mold chamber 22, in which the melted metal rapidly becomessolidified.

Immediately the metal has become solidified the drop shutter 17 isreopened and the mold tube 15 together with the mold blank is let downas indicated with the dotted line 23. After some distance of free fallthe mold 15 hits a stop bar as shown in FIG. 2. Thereby the mold gets ashock so that the blank 23 is released and drops down in the coolingliquid 14. After the molded bar has been cooled it is ready to be takenout for possible further working.

FIG. 3 shows an alternative equipment for molding of metal, whichpreferably may be combined with the crucible shown in FIG. 1. In thiscase the upper portion of the carrier 13 has an opening 24 through whichprotective gas flows from the protective gas chamber 21 and through theannular channel between the mold tube 15 and the carrier 13'. Theprotective gas leaving the opening 24 is lightened thereby giving theabove mentioned thin blue flame 11' which indicates a deficit of oxygenof the protective gas inside the carrier 13'. For molding of a metal barthe crucible in FIG. 1 is tilted so that the spout 7 with the spoutstopper 8 comes within the area of the gas flame 11', whereby air isprevented to come into contact with the molten metal. Molding andcooling otherwise is made as explained in connection to FIG. 2.

Stress-Relieving Anneal Step

After an object like a bar or a wire is molded the object is to becomestress-relieving annealed.

In FIG. 4 an apparatus for stress-relieving annealing is shown of a bar25 in an apparatus which is substantial parts coincides with theapparatus of FIG. 3. The bar 25 is carried in a verticallyreciprocatable hook 26 and can be let down through an opening in aclosed refractory furnace 28, in which the form and size of the opening27 closely coincides with the form and size of the bar 25. The furnace28 has one or more inlets 19 for the combustible gas and oxygen at somecentral portion of the furnace, and in the lower part of the furnacethere is a chimney or an outlet 29 for exiting protective gas. At thebottom of the refractory furnace 28 cooling liquid 14 is provided whichliquid preferably over a branch conduit 30 and a heat exchanger 31 iscooled and recirculated. Hot cooling liquid is removed at the upperportion of the cooling liquid chamber and chilled liquid enters at thebottom of the chamber. The bar 25 is stress-relieving annealed and issuccessively let down in the cooling liquid 14.

FIG. 5 shows an apparatus for stress-relieving annealing of a wirewithout access of air. From a supply roller 32 a wire 33 passes over apulley and enters a de-ionized water bath 34 in which the wire moves atlast in two turns over an idle running contact roller 35 of copper,graphite or carbon or similar material. By means of a driving roller 36the wire is fed from the water bath and into the area of a synchronouslydriven guide roller 37 and an idle running roller 38 which are providedat the upper portion of a protective gas channel 39. At the lower partto the protective gas channel 39 there is an inlet 40 for combustiblegas and oxygen, and at the lower part of the protective gas channelthere is also connected another water bath 41 for de-ionized water andhaving a purity, which like the purity of the water bath 34 is less than0.1 us/cm². If necessary, the two water baths 34 and 41 may contain somenon-allergy creating conductive salt for providing a spark blow-out. Inthe lower water bath 41 the wire is driven between two guide rollers andat last two turns round a driving, speed controlling contact roller 42of copper, graphite, carbon or a similar alternative material. From thecontact roller 42 the wire is fed to a winding roller 44 over a pulley43. Between the two contact rollers 35 and 42 a current is fed. Thecurrent heats the wire to a suitable temperature for stress-relievinganneal, and the annealing is made while the wire passes through theprotective gas channel 39 in which the protective gas entering the gasinlet 40 prevent the access of air.

If it is desired to prevent water steam from mixing with the protectivegas in the channel 39, a main gas outlet B is provided at or adjacentthe surface of the cooling bath, and only a minor portion of the exhaustgas is allowed to pass the channel 39 and to leave through the topoutlet A.

FIG. 6 shows an alternative embodiment for stress-relieving annealing ofa ring 45 of wound wire. In this case the annealing is made in an opencontainer 46 of a refractory material which at the top is formed with anannular tube 47 having an inlet 48 for protective gas. The circular tube47 is formed with a downwards extending annular wall 49 providing adownwards directed curtain of protective gas entering the container 46.The container 46 is mounted in an outer container 50 under gas sealedconditions. In the bottom of the outer container 50 there is a coolingbath 51 and on a level above the surface of the cooling bath there is aninlet 52 for protective gas. The inner container 46 is formed with adrop shutter 53 by which the wire ring 45 is supported. The heating ofthe wire ring to stress-relieving annealing temperature is provided by amanually or mechanically controlled burner 54 which is facing the bottomof the container 46 and the wire ring 45. From the protective gaschamber 55 above the water bath 51 protective gas leaves through a gasoutlet 56 at the top of the outer container 50, and the protective gastogether with a combustible gas from the inner part of the innercontainer 46 leaves in the direction upwards through the open containerthereby preventing air from entering the container. The exhaust gas fromthe outlet 56 may be guided to the inlet 48 and may be used for theprotective gas curtian from the gas ring 47. After stress-relievinganneal of the wire ring 46 the drop shutter 53 is opened and the wirering 45 is let down in the cooling bath 51.

Cold Working

The blank provided according to the invention may be a bar, a wire orany other object, and said blank is cold worked to any wanted shape. Thecold working does not necessitate any particular handling and is made inthe conventional way in the air.

Soldering Step

In most cases the continued treatment involves soldering of the blank,and for facilitating the continued handling and to prevent joints fromopening when subjected to soldering heating the blank isstress-relieving annealed in the above described way. As mentioned thestress-relieving anneal is made without access of air and withoutcontact with any external substances. It should be noted that thestress-relieving annealing previously was made in a heated salt bath,but according to the invention it is important that the stress-relievingannealing is done without any contact with such salts.

When soldering the cold worked and stress-relieving annealed object, forinstance a chain, solder is applied in the joints of the chain and thechain is heated until the solder melts and interconnect the ends of thejoint. Soldering can be made by means of the apparatus shown in FIG. 6,whereby the wire ring 45 is substituted by the object or objects to besolders, and immediately after soldering temperature has been reachedand the solder has melted in the joints the drop shutter 53 is openedand the soldered objects are let down in the cooling bath 51. Also inconnection to soldering it is important that the air is prevented fromgetting into contact with the hot objects, and this is effectivelyprevented in the apparatus according to FIG. 1. In this apparatus it ispossible to provide a discontinuous soldering of long chains, wherebythe chain is successively and stepwise fed down in the heating chamberunder the gas curtain 49 and the burner 54, and correspondingly thechain is stepwise let down in the cooling bath 51.

An apparatus suited for continous soldering is shown in FIG. 7. Theapparatus comprises a movable table like for instance a circular table61 which rotates at the controlled speed around a shaft 62. At oradjacent the periphery of the table there is a heating channel 63 whichis substantially sealed toward the table 61. At the inlet end 64 theheating channel 63 has a small opening 65 for entering of an object tobe stress-relieving annealed or to be soldered for instance a chain 66,which over a pully 67 is continously fed down on the table. At theoutlet end the heating channel 63 is directly connected to a coolingchannel 68, which preferably has smaller dimensions than the heatingchannel 63. The outlet hole (not shown) at the outlet end of the heatingchannel 63 is like the inlet hole 65 of small dimension for reasonswhich will be explained in the following. The cooling channel 68 shouldhave such length that the treated objects, for instance the chain 66,has a temperature when leaving the cooling channel 68 which issubstantially less than the oxidization temperature. The outlet hole 69of the cooling channel 68 is large. For heating of the chain the heatingchannel 63 has two tube connections, viz. a connection 70 at the outletend of the heating channel 68 for supply of combustible gas and someamount of oxygen and a second connection 71 at the inlet end of theheating channel 63 for removal of exhaust gases. Over a conduit 72 theexhaust gas connection 71 is directly connected to a connection 73 atthe inlet end of the cooling channel 68. The exhaust gases from theexhaust gas outlet 71 are thereby directly fed to an exhaust gas inletof the cooling channel, while being successively cooled the exhaustgases pass through the cooling channel 68 and leave through the largeoutlet hole 69. Since the heating channel 63 has a small inlet opening65 and a small outlet opening, the largest portion of the exhaust gasesare transmitted from the exhaust gas outlet 71 from the heating channel63 to the gas cooling inlet 73 of the cooling channel 68.

It may be considered necessary to cool the exhaust gases while movingfrom the exhaust gas outlet 71 to the exhaust gas inlet 73, andtherefore a cooling equipment as diagrammatically indicated in FIG. 7can be interconnected between the connections 71 and 73.

As evident the combustion gases flow in counter current to the movingdirection of the chain 66, and the chain thereby is successively heatedduring the movement from the inlet end 64 to the outlet end. The highestheat is reached adjacent the outlet end at which the solder should becompletely melted.

A stretching of the chain may cause the links to open and for avoidingsuch stretching of the chain a pusher roller 74 is provided at the inletend of the cooling channel 68. The pusher roller 74 rotates with aperipheral speed which is slightly less than the moving speed of thechain on the table 61, and the roller 74 thereby pushes the links intoeach other. This both prevents a stretching of the links and an openinggo the soldering space with the subsequent risk for bad soldering andalso prevents two links from being soldered to each other, so calledstiff soldering. Preferably the pusher roller 74 is cooled, for instanceby a fan 75 and the pusher roller thereby also contributes to a quickcooling of the chain 66.

The exhaust gases from the inlet 70 for combustible gases and oxygen andsuccessively cooled during the passage through the heating channel 63,through the connection conduit 72 and through the cooling channel 68,and the chain is successively cooled by said gases while passing throughthe cooling channel. The exhaust gases provide an effective protectivegas preventing the access of air both to the heating channel 63 and tothe cooling channel 68. By the described apparatus the stress-relievingannealing and the soldering, respectively, is made without access ofair.

For facilitating the soldering a fluxing material may be let into thesoldering chamber together with the protective gas or the heating gas.The soldering of course also can be done in that the chain is moved inan atmosphere of protective gas and in that a soldering flame is direcedto the chain while passing the said flame. As soon as the part of thechain to be soldered has passed the soldering flame the said plate issurrounded by the protective gas which prevent the air from getting intocontact with the chain and thereby prevents the metal from oxidizing andfor assimilating impurities which later may cause allergic affections.

After an object has been manufactured, polishing may be necessary.According to the invention it is not suitable that the metal gets incontact with strange substances like waxes and the like duringpolishing. The surface cleaning and the polishing rather can be carriedout in vibrating rubber containers filled with small parts of steelhaving a suitable shape and size for providing mechanical cleaning andpolishing of the manufactured product. For coarse polishing de-ionizedwater or pure alcohol or a mixture of the two liquids can be used. Bothliquids must have a purity of at least 0.1 us/cm², and there may be anaddition of powdered optimum pure chalk or a similar material.

After the coarse polishing a fine polishing must be made in the samevibrator and in the same de-ionized liquid bath and with a non-allergycreating fine polishing addition.

A final surface covering may be provided by galvanic plating basedsolely on a technique using potassium cyanide.

The chemicals of the potassium cyanide bath likewise must be made ofoptimum pure metal salts and must be continously filtered and purifiedby means of carbon filter or a corresponding purifying means, and thebath must be protected against any addition of foreign substances inthat the bath is hermetically closed. It is not allowed to add anypotassium chloride of any type to the bath, nor any acids or acidtreated products may be added. The galvanic process must under nocircumstances be speeded up by a too large flow of current. In casethere is a risk that a dialysis starts which in turn starts productionof oxygen and nitrogen gases this must be avoided.

After the product is coated according to the galvanic process, theproduct is once again fine polished in vibrating equipment as previouslyexplained. Any surface polishing should be made in a bath which preventsthe air from entering. In all surface polishing there is frictionheating, whereby the ability of the metal to assimilate impurities isincreased. The pure bath prevents such assimilation of impurities.

To the galvanic bath it is not allowed to add any other conductive saltsthat optimum pure potassium cyanide and optimum pure potassiuym cyanidebased metal salts. The concentration of the potassium cyanide and themetal salts of potassium cyanide should be on the lowest possible level.

It should be noted that only pure carbon or graphite is allowed to beused as an anode for a gold bath. The gold bath should be exchangedevery day or otherwise when consumed to a substantial part. As an anodefor a silver bath it is only allowed to use pure silver made accordingto the above description. The silver anodes must not be kept in the bathfor a longer time than necessary for maintaining the balance of thesilver content. An object manufactured according to the above describedmethod and by the above described apparatus contains just completelypure metals and has been manufactured without the addition of anyimpurities and otherwise allergy creating substances. Several years oftests have proved that objects manufactured according to the describedmethod and appartus have not in any case given the user allergicaffections or other skin diseases.

I claim:
 1. A method for manufacturing a non-allergenic metal objectwhich can be safely worn next to the skin, comprising the steps of:providing an optimum pure starting material selected from a classcomprising an optimum pure nobel metal and an optimum pure noble-metalalloy; creating a protective atmosphere at atmospheric pressure andconsisting of water-free hydrocarbons incompletely combusted with pureoxygen and free of oxygen, hydrogen, nitrogen and nitrogen oxides;melting said starting material in said protective atmosphere; molding amolded object from said starting material in said protective atmosphere;solidifying and cooling said molded object in said protectiveatmosphere; the step of annealing the solidified molded object prior tocooling and including the further steps of heating said protectiveatmosphere and causing it to flow in one direction, moving thesolidified molded object through the heated flowing protectiveatmosphere in the opposite direction, maintaining a portion of theheating flowing protective atmosphere sufficiently hot to effectannealing of the solidified molded object, and maintaining anotherportion of the heated flowing protective atmosphere sufficiently cool toallow cooling of the annealed molded object.
 2. A method according toclaim 1 including the further steps of heating said protectiveatmosphere and causing it to flow in one direction, moving thesolidified molded object through the heated flowing protectiveatmosphere in the opposite direction, maintaining a portion of theheated flowing protective atmosphere sufficiently hot to enablesoldering of the solidified molded object, and maintaining anotherportion of the heated flowing protective atmosphere sufficiently cool toallow cooling of the soldered solidified molded object.
 3. A methodaccording to claim 2 including the step of adding fluxing material tothat portion of said flowing protective atmosphere wherein solderingoccurs.
 4. A method according to claim 1 including the steps ofproviding a mold for casting the starting material, applying parrafinbased oil on the mold, employing heat from the melted starting materialentring the mold to effect gasification of the oil, and employing thegasified oil as said protective atmosphere.